The present invention is directed to a substrate which is coated with at least one layer of Magnesium-Oxide, i.e. of MgO, and which has an extent of at least 100 mmxc3x97100 mm. Further, the present invention is directed to a method for manufacturing a coated substrate and especially for manufacturing a substrate which is coated with at least one MgO-layer and which has an extent of at least 100 mmxc3x97100 mm.
Further, the present invention is directed to a coating apparatus for MgO coating planar substrates with an extent of at least 100 mm to 100 mm.
It is known to coat relatively large surface substrates, as especially substrates for Plasma Display Panels (PDP), by means of electron beam evaporation with high quality MgO-layers. The high quality is e.g. guaranteed by the fact that the density of the deposited layer material, compared with the density xcfx81 of MgO-bulk material, which is xcfx81=3.58 g/cm3, is very high, namely between 85% and 95% of the bulk material density xcfx81.
In the following, the term xe2x80x9c"THgr"-2"THgr"-methodxe2x80x9d is used.
This method is known from F. Kohlrausch, Praktische Physik, vol. 2, 23rd edition, p. 753, B. G. Teubner, Stuttgart 1985, and from Leonid V. Azaroff, xe2x80x9cElements of X-Ray Crystallographyxe2x80x9d, McGraw-Hill Book Company, New York, St. Louis, San Francisco, Toronto, London, Sydney, pp. 366-367.
Attention is further drawn to xe2x80x9cElements of X-Ray Diffractionxe2x80x9d, 2nd edition, B. D. Cullity, Addison-Wesley Publishing Company, Inc., Reading, Mass., pp. 188-189.
xe2x80x83The mentioned method resides on the xe2x80x9cBragg methodxe2x80x9d and is based on rotation of the crystal by an angle "THgr" coupled to a rotation of a detector by an angle of 2"THgr" and is thus named xe2x80x9c"THgr"-2"THgr"xe2x80x9d-method.
If, in the present application, we talk of a xe2x80x9cpeak at (xyz)xe2x80x9d we refer to a peak in the measuring diagram of the "THgr"-2"THgr"-method which is present according to a (xyz) orientation of the crystals as is customary in the art of crystallography.
If we refer to a xe2x80x9cpredominant peakxe2x80x9d we refer to such a peak in the "THgr"-2"THgr"-method measuring diagram which is higher than all other peaks in that diagram.
If we refer to the presence of a single peak in said diagram, it is automatically understood that peaks of higher order are present too. Thus, if we speak of a single peak at (111), we automatically understand that there is a second order peak present at (222).
The coating material which is deposited by electron beam evaporation has the significant drawback that it shows no predominant peak when examined by the "THgr"-2"THgr"-method.
The present invention proposes a substrate which is coated with at least one Mgo-layer and which has an extent of at least 100 mmxc3x97100 mm wherein the layer has a predominant peak in the resulting diagram of the "THgr"-2"THgr"-method. Especially if such an inventive substrate is a PDP-substrate, it is often very advantageous that the layer of this substrate has such predominant peak at (111) or has even exclusively a peak at (111). Manufacturing of such substrates is not possible by means of electron beam evaporation.
Further, and instead of a predominant peak at (111), a predominant peak may be realized at another, (xyz), angular location or, additionally to a predominant peak at (111), further peaks at other (xyz) angular locations may be present. Especially such a peak may be present at (200) and/or at (220) as predominant peak or as additional peaks.
In a preferred embodiment of the inventive substrate, the MgO-layer has an index of refraction n for which there is valid
1.5xe2x89xa6nxe2x89xa61.8,
for light in a spectral range of at least 400 nm to 800 nm or even preferably in a range of 350 nm to 820 nm.
In a further preferred embodiment, the index of refraction n in the said spectral range is
1.59xe2x89xa6nxe2x89xa61.75.
In a further preferred embodiment of the present invention the inventive substrate has a homogeneous surface roughness of the layer which is preferably between 0.5 nm RMS and 18 nm RMS, especially for a layer thickness of between 200 nm and 800 nm and measured by means of AFM (Atomic Force Microscopy).
Although the inventive substrate has, based on the inventively provided predominant peak, advantages compared with such substrates realized customarily, the inventive substrate has further and preferably a density of the layer material which is at least 80% or even at least 90% of the density xcfx81 of stoichiometric MgO-bulk material. As was mentioned above, the density of MgO-bulk material is xcfx81=3.58 g/cm3.
In a preferred embodiment, the inventive substrate has a layer wherein the MgO-material is stoichiometric.
It is further inventively proposed a method for producing a substrate, thereby preferably a substrate with at least one MgO-layer, and which has an extent of 100 mmxc3x97100 mm, which layer shows at least one predominant peak in the measuring course of the "THgr"-2"THgr"-method.
Such a method comprises the steps of flowing a working gas through at least one slit defined between two sputter-targets made of Mg towards a substrate which substrate is distant from an end-area of the slit, thereby selecting the purity of the Mg-target material to be at least 99%, and of introducing oxygen into the area between said end area of said slit and the substrate and further predetermining the substrate temperature prevailing during the coating process.
Thereby it becomes possible to realize the inventive substrate with a high coating rate, due to the inventively proposed reactive sputter coating and further with high degree of target material exploitation. Thus, it becomes possible to manufacture the inventive substrates industrially and in a very economical manner. As a working gas preferably Argon is used, and at least as a part of a reactive gas, oxygen. It has been recognized that by introducing a reactive gas substantially composed of oxygen and hydrogen there result highly desired further advantages. Thereby, the hydrogen fraction which is brought into the process atmosphere may be fed thereto, possibly together with the working gas, but especially preferred, together with the reactive gas, i.e. together with oxygen. Possibly the two fractions of reactive gas, oxygen and hydrogen, are premixed. Hydrogen is thereby introduced with a fraction of 0% (thus making use of pure oxygen as reactive gas) to 50%, related to the total reactive gas amount, whereby preferably hydrogen is inlet with a fraction of 0% to 10% of the total reactive gas amount. The advantages which are gained by making use of hydrogen are on one hand that the surface roughness of the MgO layer is influenced, and on the other hand the crystal structure thereof:
By introducing hydrogen into the process atmosphere it becomes possible to adjust the surface roughness of the layer. So it becomes possible to e.g. reduce thereby the surface roughness e.g. by an amount of 50%, for instance from 10 nm RMS to 5 nm RMS due to inletting hydrogen gas into the process atmosphere.
If e.g. in a pure oxygen reactive gas atmosphere there results a crystal structure with a predominant peak at (111), there results e.g. when inletting 0.5% hydrogen, still referred to the total reactive gas amount, a crystal structure of the MgO layer with a predominant peak at (220). When inletting 5% hydrogen a predominant peak results at (200).
Thus, it becomes possible to adjust the surface roughness as well as the crystal structure respectively of the MgO layer by means of controlled inlet of hydrogen gas to the process atmosphere.
The mentioned large areal substrates may be produced at relatively low costs and at high throughputs industrially.
An inventive and preferred coating arrangement for preferably performing the inventive method is proposed which comprises:
two Mg-targets mutually defining a slit and made of Mg-material with a purity of at least 99%;
at a first end area of the slit an anode arrangement and a gas feed arrangement connected to a gas tank arrangement containing a working gas, the gas nozzles of which being so directed that the gas is inlet not directly between the targets but towards the end thereof so as to result in turbulences;
a substrate carrier and conveyor arrangement with which a planar substrate is moved over and past said slit, distant from a second slit end area which is opposite to said first slit end area;
a further gas feed arrangement acting into the space between said second slit end area and said substrate carrier and conveyor arrangement, which further gas feed arrangement being connected to a gas tank arrangement for a reactive gas containing oxygen.